Digital FM modulators may be used for transmitting signals over a frequency modulated (FM) wave. In FM modulation, the frequency of a carrier wave varies in a continuous manner based on an analog message signal. In digital modulation, changes in the message signal include integration of the message signal followed by phase shifting of the message signal. In phase shifting of the signal in a digital FM modulator, values are chosen from a list of entries in a lookup table that conveys a different possible symbol or piece of information.
Thus, in FM modulation, a frequency of a carrier signal is varied by adding a time varying component such that the frequency may be the unmodulated carrier frequency plus a deviation from the carrier frequency with respect to the input message signal.
Typically in FM modulation, a message signal is integrated, then the integrated message signal is used to phase shift the carrier to modulate the signal. However, efficient implementation of phase shifting of the integrated message signal may be problematic in digital signal processing hardware. Also, phase shifting of the integrated message signal may be time and power consuming. For example, an input signal is received and processed and the processed input signal is then matched on a table of entries in a lookup table for phase shifting. A corresponding lookup table entry is selected to obtain the phase-shifted FM modulated signal.
FIG. 1 illustrates a typical modulator. A message signal may be integrated by an integrator 101. The output of the integrator 101 provides an integrated message signal which is used to phase shift the carrier in the phase shifter 102 and modulator 103 to result in the output modulated signal. However, phase shifting of the message signal may be both time consuming and costly as a lookup table is used to obtain the FM modulated signal. Therefore, a need exists for FM modulation in an efficient manner such that a message signal may be computed in digital signal processing hardware in a power and time-saving manner.